Extensive critical reviews have been prepared in three areas that have not been recently examined. The first considers selected aspects of spontaneous mutation, with emphasis on base mispairing schemes, directed mutation, the processing of repeated sequences in higher eukaryotic genomes, and the evolution of mutation rates. The second covers the entire literature on mutation research employing T-even bacteriophage model systems. The third covers the entire literature on DNA repair employing T- even bacteriophage model systems.